The present invention relates to a process for preparing a polyvinyl alcohol film having an excellent appearance and a polarizing film having an excellent polarizing property obtained by using the polyvinyl alcohol film.
Polyvinyl alcohol films have been generally prepared by dissolving a polyvinyl alcohol resin in a solvent, deaerating the resulting solution, forming it into a film by a solution casting method and drying the film by using a metallic heating roll and the like. The film which has passed through the above drying step is then dried by a drier to evaporate the moisture contained in the film, provided again with a predetermined amount of moisture in a humidity conditioner and rolled up around a cylindrical core tube to give a rolled up film to be put on the market. The thus rolled up polyvinyl alcohol films have been utilized for many applications as a film having an excellent shape stability. One of the useful applications is an optical film, particularly a polarizing film.
If winding of a film around a cylindrical core is too slack or too tight, a problem arises in appearance of the film such that wrinkles generate or the film scratches, or a problem arises that the wound film causes blocking. If a polarizing film is produced from a film that has once caused such a problem, the polarizing property is of course deteriorated.
It is an object of the present invention to provide a process for preparing a polyvinyl alcohol film according to which generation of wrinkles and scratches and blocking of a film are prevented, thus providing an optically homogeneous polyvinyl alcohol film having an excellent appearance.
Another object of the present invention is to provide a polarizing film having an excellent polarizing property.
These and other objects of the present invention will become apparent from the description hereinafter.